Simultaneous reduction in NOx and carbon in ash from using manganese in coal burners

ABSTRACT

The present invention relates to an additive and method to simultaneously reduce both the carbon in ash and the NOx production levels resulting from the combustion of coal by the use of at least one manganese-containing additive. Use of a manganese-containing additive in a coal burning utility furnace results in both a lower carbon in ash content and lower NOx emissions.

FIELD OF THE INVENTION

The present invention relates to an additive and a method forsimultaneously reducing the production of both NOx and carbon in ashfrom the combustion of fuel containing coal by means of adding to thefuel an effective amount of a manganese compound.

BACKGROUND

When burning fuels such as fuel oil and coal in boilers, incinerators,and utility furnaces, the ability to achieve high combustion efficiencyand low emissions is of paramount importance. One of the most directways to improve combustion efficiency is to increase the volume ofcombustion air in order to ensure a complete oxidation of carbon-carbon,carbon-hydrogen, and carbon-heteroatom bonds to give combustion productsof carbon dioxide and water. Higher carbon dioxide content in thecombustion products means increased combustion efficiency and also lowercarbon content in the ash. Unfortunately, an increase in the volume ofcombustion air can promote NOx formation. In other words, with increasedcombustion air, there is an inverse relationship between combustionefficiency (reduced carbon in ash) and NOx production, such that whenone is improved, the other deteriorates. This problem is particularlymanifest in combustion systems employing a recirculation of exhaustgases, such as those commonly referred to as Flue Gas Recirculation(FGR) systems. By lowering the flame temperature, FGR lowers NO_(x) atthe expense of increased carbon in ash. Conventional combustion scienceascribed to this type of combustion at ambient pressure teaches thatthere is a trade-off between NOx and unburned carbon, namely measuresthat are designed to lower NOx will inherently increase levels ofunburned carbon, and vice versa. Metal-containing additives are known toachieve one or the other, in various combustion systems, but not bothsimultaneously. Previous and conventional attempts to get around thisusually required a series of multiple methods applied to each carbonburnout and NOx independently in order to keep them under control or atacceptable levels.

SUMMARY OF THE EMBODIMENTS

In an embodiment, the present invention relates to methods to improveboth the carbon burnout (i.e., lower carbon in ash) of coal burningfacilities and the NOx production levels by the use of at least onemanganese-containing additive compound. Use of a manganese-containingadditive in a coal burning facility, such as a utility furnace, astaught herein, results in both a lower carbon in ash content and lowerNOx emissions.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide further explanation of the presentinvention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the performance of a manganese containing additive onNOx reduction.

FIG. 2 illustrates the reduction of carbon in ash and carbon monoxide bythe use of a manganese-containing additive.

DETAILED DESCRIPTION OF EMBODIMENTS

Conventional combustion science ascribed to the combustion of coal atambient pressure teaches that there is a trade-off between NOx andunburned carbon. Namely, measures that are designed to lower NOx willinherently increase levels of unburned carbon, and vice versa.

In an embodiment herein, a manganese-containing additive is combinedwith a fuel containing, inter alia, coal. The manganese-containingadditive catalyzes an improved carbon burnout (i.e. lowering carbon inash) during the entire combustion process—both in the high and lowtemperature regions of the combustion system (i.e. in the flame frontwith temperatures as high as 3600° F. and downstream of this totemperatures as low as 550° F.).

On the other hand, NOx reduction occurs only downstream of the flamefront at temperatures outside the significant thermal NOx formingtemperature range that is above 2500° F. Below about 2500°, NOx competeswith oxygen in the carbon oxidation of manganese-containing combustionbyproduct particulate (soot or fly ash). The manganese catalyzes thiscarbon oxidation reaction, which is faster when NOx is the source ofoxygen and when the temperatures fall. This carbon oxidation by NOxcatalyzed by manganese is efficacious down to a temperature of about550° F. This NOx reduction chemistry can take place on carbon-containingparticulate such as soot or fly ash, even when the combustion settingsare at a high air to fuel ratio (i.e. running at excess oxygen tostoichiometric, or fuel lean). This is because the environment at thecarbon-containing particulate is fuel rich, a condition necessary forNOx reduction. Thus, the manganese mixed with the carbon-containingparticulate (fuel-rich) is able to catalyze carbon burnout utilizingeither combustion oxygen or NOx as the oxidant. In this manner, carbonin ash is lowered simultaneously with a NOx reduction. Carbon monoxide(CO) levels also drop during use of a manganese-containing additive,showing improved combustion efficiency in converting carbon to the moreoxidized carbon dioxide combustion product.

Therefore in another embodiment herein is presented a method of reducingsimultaneously the amount of carbon in fly ash, the amount of NOx, andthe amount of carbon monoxide resulting from the combustion of coal, themethod comprising combining coal and an additive that comprises amanganese-containing compound forming a mixture thereof; and combustingsaid mixture in a combustion chamber; the manganese-containing compoundbeing present in an amount effective to reduce the amount of carbon infly ash, the amount of NOx, and the amount of carbon monoxide resultingfrom the combusting of the coal in the combustion chamber.

Yet another embodiment provides a method of simultaneously reducing boththe amount of carbon monoxide and the amount of NOx resulting from thecombustion of coal, the method comprising combining coal and an additivethat comprises a manganese-containing compound forming a mixturethereof; and combusting said mixture in a combustion chamber; themanganese-containing compound being present in an amount effective toreduce both the amount of carbon monoxide and the amount of NOxresulting from the combusting of the coal in the combustion chamber.

An additional embodiment provides a method of reducing both the amountof carbon in fly ash and the amount of NOx resulting from the combustionof coal, the method comprising combusting coal in the presence of atleast 1 ppm of a manganese-containing additive, whereby the amount ofcarbon in fly ash and the amount of NOx resulting from the combustion ofsaid coal are both reduced relative to the amounts of carbon in fly ashand NOx resulting from the combustion of coal in the absence of themanganese-containing additive.

Yet another additional embodiment provides a method for stabilizingcombustion while operating in the FGR mode. When the furnace is operatedat an FGR rate to achieve significant NOx reduction, combustioninstability is normally experienced as a result of the cooler flame dueto the FGR. This instability leads to combustion inefficiency andincreased hydrocarbon, carbon monoxide, and particulate with high carboncontent (smoke and soot). Thus is provided a method for stabilizing coalcombustion by combusting coal in the presence of at least 1 ppm of amanganese-containing additive, whereby the amount of carbon in fly ashand the amount of NOx resulting from the combustion of said coal areboth reduced relative to the amounts of carbon in fly ash and NOxresulting from the combustion of coal in the absence of themanganese-containing additive, and whereby combustion stability isimproved relative to the combustion stability of the coal in the absenceof the manganese-containing additive.

Examples of manganese-containing compounds useful herein as coaladditives include both inorganic and organometallic compounds. Inorganicmanganese compounds useful herein can include one or more of manganeseoxides, manganese sulfates, and manganese phosphates.

Preferred organometallic compounds in an embodiment of the presentinvention include alcohols, aldehydes, ketones, esters, anhydrides,sulfonates, phosphonates, naphthenates, chelates, phenates, crownethers, carboxylic acids, amides, acetyl acetonates, and mixturesthereof. Manganese containing organometallic compounds include manganesetricarbonyl compounds. Such compounds are taught, for example, in U.S.Pat. Nos. 4,568,357; 4,674,447; 5,113,803; 5,599,357; 5,944,858 andEuropean Patent No. 466 512 B1.

Suitable manganese tricarbonyl compounds which can be used includecyclopentadienyl manganese tricarbonyl, methylcyclopentadienyl manganesetricarbonyl, dimethylcyclopentadienyl manganese tricarbonyl,trimethylcyclopentadienyl manganese tricarbonyl,tetramethylcyclopentadienyl manganese tricarbonyl,pentamethylcyclopentadienyl manganese tricarbonyl, ethylcyclopentadienylmanganese tricarbonyl, diethylcyclopentadienyl manganese tricarbonyl,propylcyclopentadienyl manganese tricarbonyl, isopropylcyclopentadienylmanganese tricarbonyl, tert-butylcyclopentadienyl manganese tricarbonyl,octylcyclopentadienyl manganese tricarbonyl, dodecylcyclopentadienylmanganese tricarbonyl, ethylmethylcyclopentadienyl manganesetricarbonyl, indenyl manganese tricarbonyl, and the like, includingmixtures of two or more such compounds. One example is thecyclopentadienyl manganese tricarbonyls which are liquid at roomtemperature such as methylcyclopentadienyl manganese tricarbonyl,ethylcyclopentadienyl manganese tricarbonyl, liquid mixtures ofcyclopentadienyl manganese tricarbonyl and methylcyclopentadienylmanganese tricarbonyl, mixtures of methylcyclopentadienyl manganesetricarbonyl and ethylcyclopentadienyl manganese tricarbonyl, etc.

Preparation of such compounds is described in the literature, forexample, U.S. Pat. No. 2,818,417, the disclosure of which isincorporated herein in its entirety.

The combustion systems that may use the manganese-containing coaladditive compounds described herein include any and all internal andexternal combustion devices, machines, engines, turbine engines,boilers, incinerators, evaporative burners, stationary burners and thelike which can combust or in which can be combusted a hydrocarbonacousfuel such as coal. Coal burning furnaces, particularly large systems,are all uniquely designed. However, most have primary air streams thatdeliver coal to and through a grinding process and eventually to thecombustion chamber in the furnace. In the furnace, there may be one ormore secondary air streams that also feed air into the combustionchamber.

The manganese-containing coal additive compound can be mixed with thecoal either before or simultaneously in the combustion chamber. Forinstance, the manganese compound may be injected into the primary airstream for mixing with the coal before the combustion chamber.Alternatively, the manganese compound may be injected with a secondaryair stream into and mixed in with the coal in the combustion chamber.Finally, the additive having the manganese compound may be injectedseparately into the coal and directly into the combustion chamber. Inany alternative, there will be conditions that cause the effectivemixture of the additive having the manganese compound in the coal sothat the manganese atoms will be present and available for catalyticactivity. The additive can be a liquid form so that it is miscible withliquid fuels and easily dispersed in the combustion air by atomizingnozzles and mild heat.

The treat rate of the manganese compound with the coal is between 1 toabout 500 ppm. An alternative treat rate is from about 5 to 100 ppmmanganese. In a further embodiment, the treat rate is 20 ppm manganeseto the coal.

The following example further illustrates certain aspects of the presentinvention but does not limit the present invention.

EXAMPLE

A test was carried out in a 300 megawatt (MW) coal-burning utilityfurnace. The testing, which lasted 46 days, was roughly split intoperiods. The first period was a baseline conducted without the use ofthe manganese-containing additive, the second was conducted with themanganese-containing additive added, and the last period was thebaseline repeat. The manganese-containing additive was injected into aflue gas recirculation stream. As a result of the introduction of themanganese-containing additive, NOx levels were observed to drop from anaverage of 189 ppm to 155 ppm, a lowering of 18%. At the same time, as aresult of the introduction of the manganese-containing additive, theamount of carbon in ash fell from an average of about 20.4% to 9.4%, adecrease of about 54%. To simultaneously lower NOx and carbon in ashwith one method or a single additive is unexpected in this type ofcombustion.

FIGS. 1 and 2 demonstrate the results of the use of amanganese-containing additive in the simultaneous lowering of carbon inash and NOx in the combustion products from the foregoing example. FIG.2 demonstrates the results of the use of a manganese-containing additivein the simultaneous lowering of carbon in ash, NOx, and carbon monoxidein the combustion products from the foregoing example. The data werecollected from a coal-fired unit burning the same coal for the entireperiod, and are based on the daily average data at 200 MW plus or minus10 MW. “GB” represents the introduction of a manganese-containing coaladditive referred to as Greenburn® 2001HF Combustion Catalyst into thecombustion unit. As can be seen from the results, there was asubstantial simultaneous reduction in NOx, carbon in ash, and carbonmonoxide. The resulting reduction in NOX was 17%, the reduction in flyash carbon content was 48%, and the reduction in flue gas carbonmonoxide was 30%.

It is to be understood that the reactants and components referred to bychemical name anywhere in the specification or claims hereof, whetherreferred to in the singular or plural, are identified as they existprior to coming into contact with another substance referred to bychemical name or chemical type (e.g., base fuel, solvent, etc.). Itmatters not what chemical changes, transformations and/or reactions, ifany, take place in the resulting mixture or solution or reaction mediumas such changes, transformations and/or reactions are the natural resultof bringing the specified reactants and/or components together under theconditions called for pursuant to this disclosure. Thus the reactantsand components are identified as ingredients to be brought togethereither in performing a desired chemical reaction (such as formation ofthe organometallic compound) or in forming a desired composition (suchas an additive concentrate or additized fuel blend). It will also berecognized that the additive components can be added or blended into orwith the base fuels individually per se and/or as components used informing preformed additive combinations and/or sub-combinations.Accordingly, even though the claims hereinafter may refer to substances,components and/or ingredients in the present tense (“comprises”, “is”,etc.), the reference is to the substance, components or ingredient as itexisted at the time just before it was first blended or mixed with oneor more other substances, components and/or ingredients in accordancewith the present disclosure. The fact that the substance, components oringredient may have lost its original identity through a chemicalreaction or transformation during the course of such blending or mixingoperations or immediately thereafter is thus wholly immaterial for anaccurate understanding and appreciation of this disclosure and theclaims thereof.

At numerous places throughout this specification, reference has beenmade to a number of U.S. patents, published foreign patent applicationsand published technical papers. All such cited documents are expresslyincorporated in full into this disclosure as if fully set forth herein.

This invention is susceptible to considerable variation in its practice.Therefore the foregoing description is not intended to limit, and shouldnot be construed as limiting, the invention to the particularexemplifications presented hereinabove. Rather, what is intended to becovered is as set forth in the ensuing claims and the equivalentsthereof permitted as a matter of law.

Patentee does not intend to dedicate any disclosed embodiments to thepublic, and to the extent any disclosed modifications or alterations maynot literally fall within the scope of the claims, they are consideredto be part of the invention under the doctrine of equivalents.

1. A method of reducing both the amount of carbon in fly ash and theamount of NOx resulting from the combustion of coal, the methodcomprising combining coal and an additive that comprises amanganese-containing compound forming a mixture thereof; and combustingsaid mixture in a combustion chamber; the manganese-containing compoundbeing present in an amount effective to reduce both the amount of carbonin fly ash and the amount of NOx resulting from the combusting of thecoal in the combustion chamber.
 2. The method as described in claim 1,wherein the manganese compound is an organometallic compound.
 3. Themethod as described in claim 2, wherein the organo portion of theorganometallic compound is derived from a material selected from thegroup consisting of alcohols, aldehydes, ketones, esters, anhydrides,sulfonates, phosphonates, naphthenates, chelates, phenates, crownethers, carboxylic acids, amides, acetyl acetonates and mixturesthereof.
 4. The method described in claim 2, wherein the organometalliccompound comprises methylcyclopentadienyl manganese tricarbonyl.
 5. Themethod described in claim 2, wherein the manganese compound is selectedfrom the following group: cyclopentadienyl manganese tricarbonyl,methylcyclopentadienyl manganese tricarbonyl, dimethylcyclopentadienylmanganese tricarbonyl, trimethylcyclopentadienyl manganese tricarbonyl,tetramethylcyclopentadienyl manganese tricarbonyl,pentamethylcyclopentadienyl manganese tricarbonyl, ethylcyclopentadienylmanganese tricarbonyl, diethylcyclopentadienyl manganese tricarbonyl,propylcyclopentadienyl manganese tricarbonyl, isopropylcyclopentadienylmanganese tricarbonyl, tert-butylcyclopentadienyl manganese tricarbonyl,octylcyclopentadienyl manganese tricarbonyl, dodecylcyclopentadienylmanganese tricarbonyl, ethylmethylcyclopentadienyl manganesetricarbonyl, indenyl manganese tricarbonyl, and the like, includingmixtures of two or more such compounds.
 6. The method of claim 1,wherein the manganese-containing compound is selected from the groupconsisting of manganese oxides, manganese sulfates, and manganesephosphates.
 7. The method as described in claim 1, wherein the manganesecompound comprises about 20 ppm of the coal.
 8. The method as describedin claim 1, wherein the manganese compound comprises about 5 to 100 ppmof the coal.
 9. The method as described in claim 1, wherein themanganese compound comprises about 1 to 500 ppm of the coal.
 10. Themethod as described in claim 1, wherein the additive is introduced intoan air stream that carries the coal into the combustion chamber.
 11. Amethod of reducing both the amount of carbon in fly ash and the amountof NOx resulting from the combustion of coal, the method comprisingcombining coal and an additive that comprises a manganese-containingcompound forming a mixture thereof; and combusting said mixture in acombustion chamber; the manganese-containing compound being present inan amount effective to reduce both the amount of carbon in fly ash andthe amount of NOx resulting from the combusting of the coal in thecombustion chamber, wherein the additive is introduced directly into thecombustion chamber separately from the coal.
 12. The method as describedin claim 11, wherein the additive is introduced into a flue gasrecirculation stream.
 13. The method as described in claim 11, whereinthe additive is introduced into a secondary air stream that is deliveredinto the combustion chamber.
 14. A method of reducing both the amount ofcarbon in fly ash and the amount of NOx resulting from the combustion ofcoal, the method comprising: combining coal and an additive thatcomprises a manganese compound to form a mixture thereof; introducingthe mixture of coal and additive into a coal burning combustion chamber;combusting the mixture in the combustion chamber; and the manganesecompound being present in an amount effective to reduce both the amountof carbon in fly ash and the amount of NOx resulting from the combustionof the coal in the combustion chamber.
 15. A coal additive for use inreducing both the amount of carbon in the fly ash and the amount of NOxresulting from the combustion of coal, the additive comprising amanganese compound wherein the manganese compound is added to the coalprior to combustion at a treat rate of about 1 to 500 ppm of the coal.16. The coal additive as described in claim 14, wherein the manganesecompound is added to the coal prior to combustion at a treat rate ofabout 5 to 100 ppm of the coal.
 17. The coal additive as described inclaim 14, wherein the manganese compound is added to the coal prior tocombustion at a treat rate of about 20 ppm of the coal.
 18. A method ofreducing simultaneously the amount of carbon in fly ash, the amount ofNOx, and the amount of carbon monoxide resulting from the combustion ofcoal, the method comprising combining coal and an additive thatcomprises a manganese-containing compound forming a mixture thereof; andcombusting said mixture in a combustion chamber; themanganese-containing compound being present in an amount effective toreduce the amount of carbon in fly ash, the amount of NOx, and theamount of carbon monoxide resulting from the combusting of the coal inthe combustion chamber.
 19. A method of reducing both the amount ofcarbon monoxide and the amount of NOx resulting from the combustion ofcoal, the method comprising combining coal and an additive thatcomprises a manganese-containing compound forming a mixture thereof; andcombusting said mixture in a combustion chamber; themanganese-containing compound being present in an amount effective toreduce both the amount of carbon monoxide and the amount of NOxresulting from the combusting of the coal in the combustion chamber. 20.A method of reducing both the amount of carbon in fly ash and the amountof NOx resulting from the combustion of coal, the method comprisingcombusting coal in the presence of at least 1 ppm of amanganese-containing additive, whereby the amount of carbon in fly ashand the amount of NOx resulting from the combustion of said coal areboth reduced relative to the amounts of carbon in fly ash and NOxresulting from the combustion of coal in the absence of themanganese-containing additive.
 21. A method for stabilizing coalcombustion by combusting coal in the presence of at least 1 ppm of amanganese-containing additive, whereby the amount of carbon in fly ashand the amount of NOx resulting from the combustion of said coal areboth reduced relative to the amounts of carbon in fly ash and NOxresulting from the combustion of coal in the absence of themanganese-containing additive, and whereby combustion stability isimproved relative to the combustion stability of the coal in the absenceof the manganese-containing additive.